Pournelle was using a microcomputer to write, then, as was Gerrold. Word processors of the time didn't try to keep a whole chapter in memory, and Pournelle famously started using a home computer to write novels in 1977.

yes, it bears repeating that text editors didn't keep entire documents resident in memory, they maybe buffered a page ahead and behind.

when it appeared as a feature, spell checking was impressive for the technical feat of compressing word lists with tens of thousands of entries into representations suitable for tiny memories.